main.dart

import 'package:flutter/material.dart';

void main() => runApp(const MyApp());

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Calculator',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const CalculatorHomePage(),
    );
  }
}

class CalculatorHomePage extends StatefulWidget {
  const CalculatorHomePage({super.key});

  @override
  _CalculatorHomePageState createState() => _CalculatorHomePageState();
}

class _CalculatorHomePageState extends State<CalculatorHomePage> {
  final TextEditingController _controller = TextEditingController();
  double _num1 = 0, _num2 = 0, _result = 0;
  String _operator = '';

  void _updateControllerText(String text) {
    _controller.text = text;
  }

  void _calculateResult() {
    if (_operator == '+') {
      _result = _num1 + _num2;
    } else if (_operator == '-') {
      _result = _num1 - _num2;
    } else if (_operator == '*') {
      _result = _num1 * _num2;
    } else if (_operator == '/') {
      if (_num2 != 0) {
        _result = _num1 / _num2;
      } else {
        _result = 0;
      }
    }
    _updateControllerText(_result.toString());
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Calculator'),
      ),
      body: Padding(
        padding: const EdgeInsets.all(20.0),
        child: Column(
          children: [
            TextField(
              controller: _controller,
              readOnly: true,
              decoration: const InputDecoration(
                border: OutlineInputBorder(),
              ),
            ),
            const SizedBox(height: 20),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [
                _buildNumberButton('7'),
                _buildNumberButton('8'),
                _buildNumberButton('9'),
                _buildOperatorButton('/'),
              ],
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [
                _buildNumberButton('4'),
                _buildNumberButton('5'),
                _buildNumberButton('6'),
                _buildOperatorButton('*'),
              ],
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [
                _buildNumberButton('1'),
                _buildNumberButton('2'),
                _buildNumberButton('3'),
                _buildOperatorButton('-'),
              ],
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [
                _buildNumberButton('0'),
                _buildNumberButton('.'),
                _buildEqualButton(),
                _buildOperatorButton('+'),
              ],
            ),
          ],
        ),
      ),
    );
  }

  Widget _buildNumberButton(String text) {
    return Expanded(
      child: ElevatedButton(
        onPressed: () {
          if (_operator.isEmpty) {
            _num1 = _num1 * 10 + int.parse(text);
          } else {
            _num2 = _num2 * 10 + int.parse(text);
          }
          _updateControllerText(_num1.toString() + _operator + _num2.toString());
        },
        child: Text(text),
      ),
    );
  }

  Widget _buildOperatorButton(String text) {
    return Expanded(
      child: ElevatedButton(
        onPressed: () {
          _operator = text;
          _updateControllerText(_num1.toString() + _operator);
        },
        child: Text(text),
      ),
    );
  }

  Widget _buildEqualButton() {
    return Expanded(
      child: ElevatedButton(
        onPressed: _calculateResult,
        child: const Text('='),
      ),
    );
  }
}